Psoriasis vulgaris is a human inflammatory skin disorder characterized by tissue infiltration with IL-2R+ lymphocytes and marked epidermal changes. We propose that psoriasis is a primary immune-mediated disorder, as clinical and pathological disease features can be reversed by treatment with DAB389IL-2, a novel fusion toxin which reacts only with cells expressing high affinity IL-2R. Our major hypothesis is that psoriasis is an autoimmune disease that is caused by a response of epidermal keratinocytes to lL-2R+ tissue infiltrating leukocytes, most probably CD8+CD25+TIA-1+ cytotoxic effectors, cells that we have identified in large numbers in diseased epidermis. The specific aims of this proposal are: 1. To establish the specific ability of DAB389IL-2 to delete T-lymphocytes bearing lL-2 receptors from diseased tissue and to correlate changes in tissue-infiltrating leukocytes with quantitative and qualitative alterations in other cellular features of psoriatic pathology. 2. To determine changes in the activational and functional state of cutaneous leukocytes during treatment with DAB389IL-2. 3. To determine the effect of DAB-lL-2 therapy on the number and function of lL-2 reactive T cells that can be cloned from skin biopsies. Using a series of validated markers to quantify the extent of clinical disease, we propose to relate therapeutic improvements to number, function, and activation state of specific leukocyte subsets in psoriatic tissue. We will employ sensitive immunohistochemical approaches on cryostat-prepared tissue sections, and we will assess functional activation of disease-related leukocytes through a new technique that allows us to recover viable leukocytes from psoriatic tissues. We will establish whether DAB389IL-2 depletes effector CD8+ lymphocytes from psoriatic tissues, and/or whether this agent acts on antigen presenting dendritic cells or CD4+ lymphocytes. The possibility that DAB389IL-2 alters production of inflammatory cytokines and immunoregulatory cytokines will be explored by cloning and analysis of disease-associated T- lymphocytes before and after therapy by limiting dilution approaches. The study of psoriasis as a model autoimmune disease is advantageous because (1) psoriasis is the most common human autoimmune disorder, affecting 2-3% of the population, (2) disease activity in psoriasis vulgaris is relatively stable, allowing for study of relatively small patient populations to establish significance of outcomes, (3) clinical disease activity is visible and can be quantified by validated measures and non-invasive imaging, (4) lesional and non-lesional tissue is readily available for comparative laboratory studies, (5) target epithelial cells can be readily cultured in vitro to examine interactions with effector leukocytes or immune-derived cytokines, and (6) enriched, functional populations of tissue-infiltrating leukocytes can be obtained for direct study by a novel organ culture system.